LPG is used both in various types of industrial installations and in households. From the viewpoint of a gas supplier acquiring new clients and keeping the old ones requires continuous monitoring the actual gas consumption as well as gas level in tanks. These measurements are carried out either periodically in predetermined cycles or on demand, while the measurement results are either determined by visual inspection of rotatable indicator dials provided in measurement heads mounted on the tanks or are transmitted telemetrically.
In mechanical float level gauges commonly used nowadays an element floating on surface of a liquid gas (or other liquid medium) is arranged on a rotating arm provided with a gear transforming the arm rotation in a horizontal axis to a corresponding rotation of a vertically arranged element around a vertical axis. At the uppermost point of the rotating vertical element, in a possibly small distance from the float level gauge head made of magnetically inert material and tightly closing the tank opening, a magnet is arranged, so that magnetic field changes direction corresponding to rotation of the vertical element. A magnetic dial a scale defining the tank filling degree in form of a magnetic dial is mounted on the float level gauge head. A rotary element such as dial disc or a gauge pointer is changing its position according to the changes of the magnetic field direction, and thus showing the floating element position corresponding to the liquid medium present in the tank. Such float level gauges are considered reliable due to relatively simple mechanical construction, but they require direct visual inspection of the dial to retrieve the actual gas level status.
US 2004/0079152 A1 discloses an electrical system for measuring liquid gas amount in a tank, the system comprising a set of magnetic sensors, a temperature measurement module provided with a microprocessor with a radio module, wherein magneto-resistive transducers of magnetic field are used, having sensitivity higher than Hall effect sensors (can determine smaller fields), but being capable of measuring only small field ranges. Radio module allows to send measurement results to a remote location. However, even use of a few magnetic sensors arranged in various distance from the magnet does not guarantee a reliable operation in case of various types of level indicators.
US 2006/243345 A1 discloses a wireless tank level monitoring system utilizing a Hall effect sensor and having a base station with a battery status control connected to a radio module.
Further, in US 2004/0129075 A1 a remote fluid level detection system is disclosed, wherein a microcontroller-based electronic circuit comprising a magnetic field sensor (such as GMR AA002-02 available from NVE Corporation) detects orientation of the magnetic field generated by a single permanent magnet inside the existing gauge mechanism. The system includes a tank module comprising a housing, a battery cover, battery units, a microcontroller, a circuit board, an RF transmitter, a magnetic sensor, an attachment band, electrical connection wires, a momentary switch, an electric inclinometer, a liquid crystal display, a clock oscillator, and a voltage regulator. The tank module housing is dimensioned to fit over the pre-existing tank gauge and is secured to the gauge by means of the attachment band. The gauge is mounted on the top of the tank by mounting bolts, connecting the gauge housing to the tank, and the gauge face comprises a simple compass tracking the magnet position.
Yet further, US 2009/0243863 A1 discloses a cellular tank level monitor for liquefied gas and cryogenic liquids, the monitor being configured to be magnetically attached to the fuel tank and operatively connected to a Hall effect module.
US 2009/0160674 A1 discloses a wireless telemetry system consisting of a sensor (such as a customary Hall effect sensor) generating an electrical signal indicative of the level and/or usage, a wireless transmitter transforming this signal into an signal compatible with Wi-Fi (802.11a/b/g/n) transmission protocol, and a Wi-Fi wireless router receiving this WiFi signal and storing it on a host computer for subsequent transmission to a server computer located at a distant location over the public internet.
Moreover, in U.S. Pat. No. 6,679,116 B2 a liquid level gauge, assembly including a dial assembly having a shaped magnet and a removable magnetic detector with a Hall effect sensor. In this assembly the Hall effect sensor is connected to a dial with a cable. Further, a measurement of magnetic field is based on detection of rotation of a shaped magnet being magnetically coupled to a tank (gauge) magnet rotating in response to movements of the float arm.
U.S. Pat. No. 8,294,457 B2 discloses a rotary magnetic encoder assembly comprising a magnetic field sensor arrangement, a rotatable magnet disposed adjacent the magnetic field sensor arrangement and having a magnetic field that is sensible by the magnetic field sensor arrangement, and a rotary encoder shaft that effects rotation of the rotatable magnet without contacting the rotatable magnet.
In U.S. Pat. No. 6,564,632 B2 a liquid level gauge assembly is disclosed including a dial assembly having a shaped magnet and a removable magnetic detector with a magnetic sensor, preferably a Hall sensor. The dial assembly is capable of providing both visual and electrical output signal related to the liquid level measured by the gauge assembly. The shaped magnet has a variable thickness which, in cooperation with the Hall sensor, provides a linear output signal from the detector over more than 270 degrees. The dial assembly cover is provided with a cover having a channel-like socket adapted for receiving a Hall sensor-containing detector connected by an electric cable to external devices.
Despite numerous systems for measuring liquid gas level using magnetic field sensors and wirelessly transmitting the measurement results to a remote location there is a constant need for further improvements. The areas of improvements involves optimizing the balance between sensitivity and measurement range of a magnetic field sensor, eliminating the elements prone to damage (such as cables connecting component modules of the measurement system), increasing safety of utilizing the liquid gas level measuring systems and also reducing costs of manufacturing of and installing such smart metering devices.
The above-mentioned safety-related issues include the following problem. Several prior art liquid gas level smart metering devices are formed so as to be mounted on a float level gauge head in place of a simple mechanical dial gauge, which require visual inspection. As a rule such installation is made by means of two cross screws going through two corresponding lugs provided in the lower part of the device housing and engaging the respective threaded holes in the level gauge head. Many end users tend to replace the analogue dial indicators with such devices on their own, using inappropriate tools (such as multi-purpose tools instead of dedicated screwdrivers) or even erroneously manipulating other screws (such as hex(interior) screws commonly used to fix the level gauge head to a tank). This involves increased risk of damaging the devices, unsealing the tanks, dismantling the gauge and releasing the gas, which eventually may result in an explosion. Thus, a need has been observed and identified by the present inventors to provide a system that would allow the end users to change the sensor devices easily (for example in order to replace batteries or damaged electronic modules), while eliminating the need for detaching/attaching modules directly connected to a pressurized gas tank.